Many modern production and warehousing facilities require the storage and retrieval of thousands of inventoried items. Often goods must be stored in bins or containers due to their size or delicate construction. Therefore, storage requires loading the containers and delivering them to a known location where they can later be retrieved as necessary. When an order is received, the desired items must be retrieved from their respective positions and kitted, prepared for shipping, or otherwise put to use. An efficient storage operation requires the ability to both store and retrieve a wide variety of goods and to rapidly and effectively dispose of the retrieved items. Heretofore, a wide variety of warehousing/distribution systems have been proposed to reduce the labor required in warehousing operations. However, few systems have addressed both the storage and production requirements for a global distribution solution.
Conventional storage and retrieval systems utilize large multi-level fixed storage shelves in combination with an extractor or picking mechanism that must travel to a particular shelf to pick the desired inventory item. For example, U.S. Pat. Nos. 3,402,835 and 3,402,836 show systems in which a mobile unit traverses along a series of stationary vertical racks. The mobile unit is equipped with means for loading and unloading the vertically based storage racks. Such systems have several drawbacks. Initially, they are limited to a small number of insertion or extraction transactions each time the extractor is operated due to the need to move the picking mechanism after each insertion or extraction operation. Additionally such systems traditionally have fixed locations for storing each type of goods received within the warehouse. This prohibits efficient space utilization since the fixed location occupies the same amount of space regardless of whether a particular inventoried item has two stock units or 2000. Indeed typical warehouses having such fixed space utilization tend to have only about 25% of their usable storage space filled at any given time. Therefore, such systems are extremely wasteful of valuable building space.
More recently, storage structures have been proposed that include a movable multi-tiered storage carousel having a large number of arrays of vertically spaced container racks arranged to form a continuous horizontally operating rack assembly which travels about a continuous horizontal track. Representative storage carousels are disclosed in U.S. Pat. Nos. 4,561,820, 4,422,554, and 3,780,852. However, such systems have numerous drawbacks which limit their feasibility in high volume operations. Most notably, in order to insert a container onto, or extract a container from a rack on the storage carousel, the carousel must be stopped adjacent to the insertion and extraction mechanism and the container disengaged or inserted. The time required to start and stop the carousel inherently limits the speed at which container insertion and extraction operations may occur. Additionally, the requirement of repeatedly starting and stopping a carousel which may carry on the order of 700,000 tons of material, can be extremely taxing in terms of both power requirements, component wear and drive motor life. Further, it is difficult to stop such a massive structure with enough control to precisely position the containers for either insertion or extraction. Therefore, there is a need for an improved automated storage and retrieval system having a storage carousel that may remain in continuous motion while containers are inserted into or extracted from its storage racks.
The approach disclosed herein includes an automated storage carousel that dispenses with the need for stopping and starting the rack assembly for loading and unloading containers from the storage racks.